This invention relates to a cigarette manufacturing machine of the continuous rod type, and more particularly to a conveyor system designed to form a continuous tobacco layer or filler, and to feed it to the formation means for the so-called continuous cigarette rod.
Cigarette manufacturing machines of the aforesaid type are known, which comprise a substantially vertical duct fed at its lower end by a continuous stream of tobacco particles and closed upperly by the lower branch of an air-permeable conveyor belt in the form of an endless loop passing around end rollers.
Within the loop described by said belt there is provided a chamber connected to a suction source and bounded lowerly by a wall traversed by holes or slots.
The lower branch of the conveyor, which slides in proximity to said wall, extends in the direction of its motion beyond the vertical duct outlet as far as a position, defined as the discharge position, at which it meets the feed track for a cigarette paper web.
Under the thrust of a rising air stream, the tobacco particles rise up the vertical duct and, under the effect of the suction exerted by said chamber through the perforated wall and the air-permeable belt, adhere to said branch to accumulate thereon and form a substantially uniform layer or filler of tobacco particles. This filler, which is retained by the conveyor belt by suction, is transferred from the vertical duct outlet to said discharge position, in which it is deposited on the cigarette paper web.
The paper web is then progressively closed about the tobacco filler in order to form the so-called continuous cigarette rod.
The individual cigarettes are finally obtained from this rod by a cutting operation.
In known manner, during its passage over the path between the vertical duct and discharge position, the tobacco filler is subjected to operations the purpose of which is to increase its level of uniformity.
Its air-permeability is firstly measured by means of a control device comprising suction means.
Downstream of said control device, and controlled by it, there is provided the so-called trimmer device.
Its purpose is to reduce the transverse dimensions of the tobacco filler and at the same time to eliminate any variations in its thickness by removing a quantity of tobacco which depends on the permeability variations detected by the control device.
In such manufacturing machines of known type, the tobacco layer or filler is properly compact and perfectly adheres to the conveyor belt over that portion of the path at the vertical duct outlet. In contrast, over that portion of the path between the vertical duct and the discharge position, there is an obvious relaxing of the tobacco filler and a reduction in its adherence to the conveyor belt.
This situation is due mainly to the fact that at the vertical duct outlet, the action of the rising air stream which feeds the tobacco is added to the suction exerted on the filler by said chamber, whereas over that portion of the path outside the duct, the tobacco filler is subjected only to the suction action of said chamber.
The consequence of this is that the tobacco particles can separate from the conveyor belt.
Moreover, because of its relaxation and poor adhesion to the conveyor belt, the tobacco filler when external to the vertical duct is not in a suitable state for subjection to the air permeability control device and scraper device.